A water supply apparatus, which is installed in an apartment house or a building, is a device for supplying water to respective water terminals. In the water supply apparatus, it is a common technique to operate a pump at variable speeds by using an inverter that converts frequency and voltage of a commercial AC power supply to desired frequency and voltage. The inverter is capable of changing rotational speed of a motor, which drives the pump, as desired. Therefore, the pump can be operated at an optimal rotational speed corresponding to a load, and energy can be saved compared to a case of operating the pump at a rated speed.
This type of water supply apparatus may have a plurality of pumps controlled by using a plurality of inverters. In this case, a control substrate is provided for controlling these pumps and inverters. In the water supply apparatus using pumps and inverters, when a failure (e.g., leakage of electricity, overcurrent, or open-phase) occurs in one pump, water supply operation is switched to another pump automatically, so that water failure can be avoided.
Japanese laid-open patent publication No. 2005-351267 discloses a water supply apparatus that never fails to supply water. In this apparatus, when a control substrate for controlling pumps and inverters stops functioning properly due to some causes during water supply operation, backup operation is performed so as to switch the faulty control substrate to a control substrate in a standby state.